Cable Diversity for Induction Hob

Unless the instructions require otherwise, I would use a 32 amp circuit, and cable to suit, probably 4.0 mm. A 20 amp circuit is probably sufficient, but is it worth the risk of complaint or call backs if it trips ?


Use of the traditional diversity rule for a cooker may not be entirely reliable. A traditional cooker includes an oven and a grill, but the appliance in question is only a hob.

Andy


I have just had squint at the current edition of the OSG and think it needs a bit of a re-write.


JP

Yes, there are several bits where that would be useful, John.


David

Thank you guys, I’m finding this all very interesting! 


This is the Hob in question. Plenty of spare ways in the CU and the run is 15mtrs. I think having done some research and with your guidance. I will install a 6mm T+E and add a 40amp MCB. I think having the extra amperage may be beneficial.
https://www.electrolux-ui.com//DocumentDownLoad.aspx?DocURL=2018\\867\\346533umEN.pdf

AEG are very naughty not to include installation instructions specific to the model - part of that doc mentions plugs and sockets, and the other half having it hard wired, clearly generic cut and paste  - utter nonsense. 

It might be fun to call them and ask for the recommended cable cross section in mm2.  (the spec they give -  H05BB-F or H03V2V2-F - just  defines types of rubber covered flex, but it is available in 1,5  2,5 and 4mm cross-sections so no help at all really)

Mike.

"Household cooking appliance"! Is it a microwave? Is it a sandwich toaster? Is it a slow cooker? Is it a George Forman grill? Or is it just a cooker? ??


I am just wondering what is beneficial about oversizing the circuit. If the cable to whatever junction box connects the T&E to the H05BB-F or H03V2V2-F flex is 6 mm² on a 40 A MCB, how will you protect the flex?

If the 6mm T+E is connected via a cooker outlet plate which is most likely rated at 45amps, then from the outlet plate to the Hob in 6mm H07BN4-F cable, then in essence, it remains as 1 length of cable. Don’t forget this circuit is 30mA RCD protected too, so there is another for of protection. From some of the research I have done and other comments I have read, installing a slightly larger cable ‘could’ (not saying it will as technology these days seems to make things smaller and use less power), allow for any future appliances.


plus you never know...one day there may very well be a George Forman, sandwich toaster, microwave slow cooker on the market. It would give you more room in your kitchen and eliminate the need for consumer unit circuits??!?

Bear in mind that a flex's cpc is the same CSA as its line conductors, while a 6mm T&E only has a 2.5mm cpc. So a L-E short will have roughly the same heating effect on a 2.5 flex's cpc as on the 6mm T&E's cpc.


The overload situation is more complex, as the manufacturer gives no indication as to what the maximum current the electronics of the unit will allow it to sink. Will it allow all 4 rings on boost (54A for 4 mins, then 50A for a further 6 minutes), or will it limit it to 31A (7.35kW) at all times? Who knows? What's the min/max OCPD required by the device? Who knows?

These forums are incredible, you guys blow my mind. I learn so much?

Would you say 6mm T+E on a 40amp MCB is perhaps over the top? I really have no opinion. Especially now you’ve mentioned that the total load of 4 hobs on the go at once (even though that is highly unlikely) calculates to be 53amps...slightly different from the manufacturers 7.35kW (31.95amps) instructions. I kinda feel a bit out of my depth with making a decision if I’m honest. In one breath I’m 4mm on a 32amp MCB, then next it’s 6mm on a 40amp MCB!!!?

In Germany the usual setup is a 2-phase supply at 16A/phase - which seem to rather neatly match the nameplate 7.35kW.  The Germans don't bother with diversity much as for their system it makes little difference (if we used the UK formula on each phase it would only reduce from 16A to 11.8A). With the UK system 32A single phase reduces to a much more economic 16.6A.


The first 10A plus 30% of the remainder (plus 5A for a socket) rule for stationary cooking appliances goes back to at least the 14th Ed (circa 1966) so has certainly stood the test of time. Even if you consider a separate hob is a little different to a conventional cooker - the difference is only the oven which is typically only around 2kW or less - so I suggest would make little difference to the outcome. (As a thought experiment, add a 2kW oven to the hob - so giving an overall nameplate rating of 9.35kW - after diversity you're still under 20A.)


If you do go for a 32A circuit - be aware that 4mm² is only suitable when clipped direct (or embedded in plaster etc) - when in a building void (e.g. between ceiling and floor above - method B) it's only rated for 30A. 32A/6mm² is a pretty standard arrangement that'll cope with the majority of cooking appliances.


   - Andy.